U.S. patent number 5,279,511 [Application Number 07/964,350] was granted by the patent office on 1994-01-18 for method of filling an electrophoretic display.
This patent grant is currently assigned to Copytele, Inc.. Invention is credited to Frank J. DiSanto, Denis A. Krusos.
United States Patent |
5,279,511 |
DiSanto , et al. |
January 18, 1994 |
Method of filling an electrophoretic display
Abstract
The present invention is a method of filling the interstice
between the anode structure and the cathode structure of an
electrophoretic image display (EPID) with a fluid dispersion
containing solid pigment particles. And more specifically, a method
of filling such EPIDs when the interstice between the anode
structure and the cathode structure is less than 0.007 inches. The
present invention method includes the steps of coating the anode
structure with pigment particles prior to the assembly of the anode
structure or cathode structure into the EPID. After the pigment
particle coated anode or cathode structure has been assembled into
the EPID, the EPID is filled with a suspension medium lacking any
pigment particles. An electrophoretic effect is then created within
the EPID causing the pigment particles to migrate away from the
anode or cathode structure they coat, thereby becoming disperse
within the suspension medium.
Inventors: |
DiSanto; Frank J. (North Hills,
NY), Krusos; Denis A. (Lloyd Harbor, NY) |
Assignee: |
Copytele, Inc. (Huntington
Station, NY)
|
Family
ID: |
25508447 |
Appl.
No.: |
07/964,350 |
Filed: |
October 21, 1992 |
Current U.S.
Class: |
445/24;
204/509 |
Current CPC
Class: |
G02F
1/1679 (20190101); G02F 1/167 (20130101) |
Current International
Class: |
G02F
1/167 (20060101); G02F 1/01 (20060101); C25D
013/00 () |
Field of
Search: |
;445/24
;204/181.7,181.6,3PE,299PE,299EC |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Mark
Assistant Examiner: Knapp; Jeffrey T.
Attorney, Agent or Firm: Plevy; Arthur L.
Claims
What is claimed is:
1. A method of filling the interstice between an anode structure
and a cathode structure in an electrophoretic image display with a
dispersion of pigment particles within a suspension medium,
comprising the steps of:
coating said anode structure with said pigment particles;
assembling said anode structure into said electrophoretic image
display after said step of coating;
filling said interstice between said anode structure and said
cathode structure with said suspension medium; and
dispersing said pigment particles coating said anode structure into
said suspension medium.
2. The method according to claim 1 wherein said step of coating
said anode structure includes utilizing said anode structure as an
electrode in producing an eletrophoretic effect in a dispersion
containing said pigment particles, said electrophoretic effect
causing said pigment particles to migrate against, and coat, said
anode structure.
3. The method according to claim 2, wherein said step of dispersing
said pigment particles includes creating an electrophoretic effect
in said electrophoretic image display whereby said pigment
particles are caused to migrate toward said cathode structure,
thereby leaving said anode structure and becoming disperse in said
suspension medium.
4. The method according to claim 3, wherein said interstice between
said anode structure and said cathode structure is 0.007 inches or
less.
5. A method of filling the interstice between an anode structure
and a cathode structure in an cathode structure in an
electrophoretic image display with a dispersion of pigment
particles within a suspension medium, comprising the steps of:
coating said anode structure with said pigment particles, said step
of coating including positioning said anode structure adjacent a
fluid reservoir means opposite a cathode means, filling said
reservoir means with a dispersion containing said pigment
particles, and applying an electrical potential to said anode
structure and said cathode means thereby utilizing said anode
structure as an electrode to cause an electrophoretic effect in
said dispersion causing said pigment particles migrate toward, and
coat, said anode structure;
assembling said anode structure into said electrophoretic image
display;
filling said interstice between said anode structure and said
cathode structure with said suspension medium; and
dispersing said pigment particles coating said anode structure into
said suspension medium by creating an electrophoretic effect in
said electrophoretic image display whereby said pigment particles
are caused to migrate toward said cathode structure, thereby
leaving said anode structure and becoming dispersed in said
suspension medium.
6. The method according to claim 5, wherein a voltage differential
of approximately 200 volts is applied between said cathode means
and said anode structure to cause said electrophoretic effect.
7. The method according to claim 5, wherein said step of
positioning said anode structure adjacent a fluid reservoir means
includes positioning said anode structure within a fixture whereby
the surface of said anode structure, which will face said
interstice within said electrophoretic image display, faces said
cathode means across said fluid reservoir means.
8. The method according to claim 7 wherein said fluid reservoir
means has a depth between said anode structure and said cathode
means of between 0.007 inches and 0.014 inches.
9. The method according to claim 7, wherein said fixture includes a
filling means through which the dispersion containing said pigment
particles can be introduced into said fluid reservoir means.
10. The method according to claim 9, wherein said step of coating
said anode structure further includes inclining said fixture
relative the horizontal so that said filling means is positioned at
the highest point on said fluid reservoir means, said step of
inclining helping the dispersion containing said pigment particles
to flow into said fluid reservoir means and providing gravity
assistance to said pigment particles so that said pigment particles
travel throughout said fluid reservoir means and away from said
filling means.
11. The method according to claim 10 wherein said fixture is
inclined at an angle of between 45 degrees and 90 degrees while
said electrophoretic effect is used to coat said anode structure
with said pigment particles.
12. A method of filling the interstice between an anode structure
and a cathode structure in an electrophoretic image display with a
dispersion of pigment particles within a suspension medium,
comprising the steps of:
coating said anode structure with said pigment particles;
drying said pigment particles coating said anode structure prior to
assembling said anode structure into said electrophoretic image
display;
assembling said anode structure into said electrophoretic image
display;
filling said interstice between said anode structure said and said
cathode structure with said suspension medium; and
dispersing said pigment particles coating said anode structure into
said suspension medium.
13. A method of filling the interstice between an anode structure
and a cathode structure in an electrophoretic image display with a
dispersion with pigment particles within a suspension medium,
comprising the steps of:
coating said anode structure with said pigment particles by
utilizing said anode structure as an electrode in producing an
electrophoretic effect in said dispersion containing said pigment
particles, said electrophoretic effect causing said pigment
particles to migrate against, an coat, said anode structure;
assembling said anode structure into said electrophoretic image
display;
filling said interstice between said anode structure and said
cathode structure with said suspension medium by submersing said
electrophoretic image display in a volume of said suspension medium
while in a chamber having a pressure less than ambient and
increasing the pressure in said chamber to ambient so that said
suspension medium flows into said interstice; and
dispersing said pigment particles coating said anode structure into
said suspension medium by creating an electrophoretic effect in
said electrophoretic image display whereby said pigment particles
are caused to migrate toward said cathode structure, thereby
leaving said anode structure and becoming dispersed in said
suspension medium.
14. A method of dispersing solid particles into a suspension fluid,
comprising the steps of coating a conductive surface with said
particles; submersing said conductive surface in a volume of said
suspension fluid after said step of coating; and
creating an electrophoretic effect in said suspension fluid using
said conductive surface as an electrode where said particles are
caused to migrate away from said conductive surface and therefore
become dispersed in said suspension fluid.
15. The method according to claim 14, wherein said step of coating
includes positioning said conductive surface within a fluid
reservoir means opposite an electrode means whereby said fluid
reservoir means separates said conductive surface from said
electrode means:
filling said fluid reservoir means with a dispersion containing
said pigment particles; and
providing an electric potential to said conductive surface and said
electrode means inducing an electrophoretic effect in said
dispersion whereby said pigment particles are caused to migrate
toward, and coat, said conductive surface.
16. The method according to claim 15 wherein said conductive
surface is an anode structure for an electrophoretic image
display.
17. The method according to claim 15 wherein said conductive
surface is a cathode structure for an electrophoretic image
display.
18. The method according to claim 15, further including the step of
inclining said fluid reservoir means during said electrophoretic
effect thereby causing said pigment particles to travel away from
their point of entry into the fluid reservoir means and
substantially evenly coat said conductive surface.
19. The methods according to claim 15, further including the step
of drying said pigment particles on said conductive surface.
20. The method according to claim 19, wherein said step of drying
includes positioning said conductive surface coated with said
pigment particles in an oven means for a predetermined period of
time.
Description
FIELD OF THE INVENTION
The present invention relates to methods of filling electrophoretic
image displays with a dispersion of dielectric pigment particles
suspended within a suspension medium, and more particularly to such
filling methods for filling electrophoretic panels having extremely
small spacings or interstices between the anode structure and
cathode structure.
BACKGROUND OF THE INVENTION
The electrophoretic effect is well known and the prior art is
replete with a number of patents and articles which use and
describe the effect. See for example, U.S. Pat. No. 5,077,157
issued on Dec. 31, 1991 and entitled Methods of Fabricating Dual
Anode Flat Panel Electrophoretic Displays. See U.S. Pat. No.
4,850,919 entitled Monolithic Flat Panel Display Apparatus and
Methods for Fabrication Thereof issued on Jul. 25, 1989, see U.S.
Pat. No. 5,505,763 entitled Dual Anode Flat Panel Electrophoretic
Display Apparatus, issued on Oct. 1, 1991. The above patents are
all assigned to CopyTele, Inc., the assignee herein with Frank J.
DiSanto and Denis A. Krusos, the named inventor and the inventors
herein. As will be recognized by a person skilled in the art, the
electrophoretic effect operates on the principle that pigment
particles, when suspended in a medium, can be electrically charged
and thereby caused to migrate through the medium to an electrode of
opposite charge. Electrophoretic image displays (EPID) utilize the
electrophoretic effect to produce desired images. In a EPID,
colored dielectric particles are suspended in a fluid medium of an
optically contrasting color. The colored electrophoretic particles
are then caused to selectively migrate against a transparent
screen, thereby displacing the fluid medium against the screen and
creating the desired image.
In a conventional EPID, a volume of an electrophoretic dispersion
is encapsulated in between an anode structure and a cathode
structure. Conventionally to create an image in an EPID, the
dielectric pigment particles in the dispersion are caused to
migrate toward the cathode structure. The cathode structure is
transparent, consequently as the pigment particles displace the
suspension fluid against the cathode structure, the desired image
can be formed. The response time of an EPID is dependent upon the
time it takes the pigment particles to migrate through the
suspension medium and reach the cathode structure. Consequently, in
an attempt to create more efficient EPIDs, EPIDs have been formed
having very small interstices in between the anode structure and
the cathode structure. Such constructions therefore lessen the
distance the pigment particles must migrate and consequently effect
the response time capabilities of the EPIDs.
A problem with EPIDs having small spacings between their anode and
cathode structures, is how to fill the EPIDs with the needed
pigment particles and suspension fluid. In EPIDs having a spacing
of 0.007 inches or more between its anode and cathode structures,
the EPID is filled by introducing a dispersion of pigment particles
and suspension fluid into the EPID chamber with a pipette filler or
similar device. However, with EPIDs having a fluid chamber with a
spacing of less than 0.007 inches, pipette filling techniques are
not as effective. With spacings of less than 0.007 inches, the
suspension fluid readily enters the fluid chamber. However, due to
their size and bulk, the pigment particles accumulate near or at
the entrance of the chamber. For EPIDs having spacing of less than
0.003 inches, the pigment particles become trapped at the point of
insertion and fail to flow altogether. Consequently, the design of
narrow chambered EPIDs is become limited by a manufacturers ability
to fill EPIDs with dispersions, thereby hindering advancements in
EPID technologies available through EPIDs having an interstice
spacing of less than 0.007 inches.
It is, therefore, a primary objective of the present invention to
provide a method of filling EPIDs having an interstice spacing of
less than 0.007 inches with a proper dispersion of pigment
particles and suspension fluid.
SUMMARY OF THE INVENTION
The present invention is a method of filling the interstice between
the anode and cathode structure of an electrophoretic image display
(EPID) with a fluid dispersion containing solid pigment particles.
And more specifically, a method of filling such EPIDs when the
interstice between the anode structure and the cathode structure is
less than typically about 0.007 inches. The present invention
method includes the steps of coating the anode structure or cathode
structure of an EPID with pigment particles prior to the assembly
of the anode structure or cathode structure into the EPID. After
the pigment particle coated anode or cathode structure has been
assembled into the EPID, the EPID is filled with a suspension
medium lacking any pigment particles. An electrophoretic effect is
then created within the EPID causing the pigment particles to
migrate away from the anode or cathode structure they coat, to
disperse within the suspension medium.
In the preferred embodiment the anode structure or cathode
structure are initially coated with the pigment particles by
utilizing the anode structure or cathode structure as an electrode
in a fluid reservoir containing a dispersion of the pigment
particles. An initial electrophoretic effect is created in the
reservoir by applying an electric potential to the anode or cathode
structure and an opposing electrode. The electrophoretic effect
created causes the pigment particles contained within the
dispersion to migrate toward, and coat the anode or cathode
structure.
Once fully coated, the electrical potential is removed and the
pigment particle coating dried. The coated anode or cathode
structure is then fabricated to form an EPID where the coating is
removed by a reversed electrophoretic effect.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, reference is
made to the following description of an exemplary embodiment
thereof, considered in conjunction with the accompanying drawings,
in which:
FIG. 1 is a cross-sectional view of a conventional electrophoretic
image display;
FIG. 2A is a top view of one preferred embodiment of a fixture used
in the present invention method;
FIG. 2B is a cross-sectional view of the embodiment of the fixture
illustrated in FIG. 2A, view along section line 2B--2B;
FIG. 3 is a cross-sectional view of an anode structure of an EPID
positioned within the fixture illustrated by FIG. 2A to facilitate
the present invention method; and
FIG. 4 is a flow chart illustrating the present invention
method.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 1, there is shown a cross section of a
conventional Electrophoretic Image Display (EPID) 10. As will be
recognized by a person skilled in the art, an EPID 10 contains a
volume of an electrophoretic dispersion 12 encapsulated between an
anode structure 14 and a cathode structure 16. The cathode
structure 16 is comprised of a glass plate 17 on which is deposited
a thin layer 18 of indium-tin-oxide (ITO) or a like compound. The
ITO layer 18 is deposited in such a manner so as to be
substantially transparent when viewed through the glass plate 17. A
cathode grid 20 is etched onto the ITO layer 18 in a grid-like
pattern, providing the configuration needed to selectively create
images whereby the spacing of the cathode grid 20 controls the
resolution of any viewed image.
The electrophoretic dispersion 12 is comprised of dielectric
pigment particles 22 suspended in a suspension fluid 24 of a
contrasting color. The volume of the electrophoretic dispersion 12
contained by the EPID 10 is contained within the interstice D
located in between the anode structure 14 and cathode structure 16.
In the present embodiment of the EPID 10 the interstice D between
the anode structure 14 and cathode structure 16 is typically 0.007
inches or less. However, it should be understood that the present
invention filling method can be applied to any EPID regardless to
the size of the spacing in between its anode and cathode.
Referring to FIGS. 2A and 2B, a fixture 30 is shown for use in
coating either the cathode structure 16 or the anode structure 14
of EPID 10 with pigment particles 22. The fixture 30 is formed from
a continuous dielectric material 32, such as MYLAR or a similar
fluid impervious material, being placed around the periphery of a
sheet of glass 34 that is coated with a layer 39 of
indium-tin-oxide (ITO). The material 32 forms a frame for the ITO
coated glass sheet 34. As a result of the placement of the
dielectric material 32, only an inner region 38 of the ITO coating
39 is exposed. The dielectric material 32 creates a substantially
fluid impervious seal against the ITO coating 39. As such the inner
region 38 defined by the dielectric material 32 becomes a fluid
reservoir. The dielectric material 32 used to define the inner
region 38 is at least 0.007 inches thick, and is preferably
approximately 0.014 inches thick. In any event, their dimensions
may vary accordingly. Consequently, the inner region 38 defined by
the dielectric material 32 can retain fluid to a depth of between
0.007 inches and 0.014 inches, depending upon the thickness of the
dielectric material 32 used. Furthermore, the size of the inner
region 38 defined by the dielectric material 32 is formed to be at
least as large as the image area of the EPID to be filled.
It should be understood that the use of a dielectric material 32,
such as MYLAR, upon the ITO coated glass 34 is merely exemplary,
and functional equivalents may be used. More specifically, in
forming the fixture 30, various conductive substrates can be used
in place instead of the ITO coated glass 34. Similarly, other
dielectric materials could be used in place and stead of MYLAR,
provided the dielectric materials forms a substantially fluid
impervious seal against the below lying conductor substrate.
When manufacturing the EPID 10 of FIG. 1 the anode structure 14,
prior to assembly into the EPID 10, is placed atop the fixture 30.
Referring now to FIG. 3, in conjunction with the flow chart
expressed in FIG. 4, the present injunction method can be
described. In FIG. 3 the anode structure 14 is shown atop the
fixture 30. The fixture 30 is angled above the horizontal by an
angle of inclination A. As indicated by block 41, the anode
structure 14 is placed atop the fixture 30 so that the area of the
anode structure 14 corresponding to the image area of the EPID 10
is above the inner region 38 defined by the dielectric material 32.
Additionally, the anode structure 14 is positioned atop the fixture
30 in such a manner so that the anode structure 14 does not
completely cover the inner region 38 defined by the dielectric
material 32 and an opening 40 exists through which the inner region
38 can be accessed below the anode structure 14. The fixture 30 is
angled so that the opening 40 occurs adjacent the most elevated
edge of the anode structure 14.
As shown in FIG. 3, the ITO layer 39 of the fixture's glass
substrate 17 is coupled to the negative terminal of a power supply
44. Similarly, the anode structure 14 is coupled to the positive
terminal of the same power supply 44. The circuit between the ITO
layer 39 and the anode structure 14 remains open because the
dielectric material 32 separates the anode structure 14 from the
ITO layer 39, electrically isolating both components. Additionally,
a switch 46 may be placed in the circuit to control the flow of
electricity from the power supply 44.
In the shown embodiment a metal plate 48 is placed atop the anode
structure 14 on the surface facing away from the fixture 30 and is
taped or otherwise removably adhered to the anode structure 14. A
magnet 50 is then placed atop the metal plate 48 to serve as a
holder. The metal plate 48 and magnet 50 act as a handle means to
help in the manipulation of the anode structure 14 to and from the
fixture 30. It should also be understood that any other handle
means may be used provided the handle means does not compromise the
integrity of the anode structure 14.
With the switch 46 turned to the "off" position, a dispersion of
pigment particles and suspension fluid are introduced into the
opening 40 as indicated by arrow 52. The introduction of the
dispersion, expressed by block 43 of the flow chart, is made
utilizing a pipette or other similar controlled fluid distributing
device. During the introduction of the dispersion through the
opening 40, the fixture 30 should be inclined at an angle of
approximately twenty degrees with the horizontal. As a result of
the angle of inclination A, the dispersion introduced through the
opening fills the inner region 38 under the anode structure 14 as
defined by the confines of the dielectric material 32. The inner
region 38 consequently fills with the dispersion being confined by
the anode structure 14 on the top, the ITO layer 39 on the bottom
and the dielectric material 32 at the sides.
Once the inner region 38 is completely filled with the dispersion
the switch 46 is turned to the "on" position. As a result, the ITO
layer 39 is held at a negative potential and the anode structure 14
is held at a positive potential. In the preferred embodiment the
power supply 44 should supply a voltage of approximately two
hundred and thirty volts. As a result of the electrical potential
supplied to both the ITO layer 39 and the anode structure 14, an
electrophoretic effect is induced within the inner region 38 below
the anode structure 14. The electrophoretic effect, as indicated by
block 45 in the flow chart, thereby causes the pigment particles
within the dispersion to migrate to the anode structure 14.
After the initial thirty seconds or so of the induced
electrophoretic effect, the angle of inclination A is increased to
between 45 degrees and 90 degrees, depending upon the depth of the
inner region 38. For instance, if the dielectric material 32 used
is 0.014 inches deep, the fixture 30 need only be inclined to an
angle of 45 degrees to ensure the flow of fluid out of inner region
38. However, if the dielectric material 32 used is 0.007 inches
thick and the inner region 38 is only 0.007 inches deep, the
fixture 30 may be inclined to an angle of 90 degrees to ensure the
flow of fluid out of inner region 38. Once inclined at the
appropriate angle, the electrophoretic effect is allowed to
continue in the inclined position for a predetermined period of
time, which is preferably about thirty minutes.
After the thirty minute period has elapsed, the angle of
inclination A is again reduced to approximately 20 degrees and the
switch 46 is turned to the "off" position thereby ending the
electrophoretic effect. At this point, as indicated by block 47,
the anode structure 14 can be removed from the fixture by
manipulating the magnet handle 50 on the anode structure 14. The
effect of the electrophoretic effect on the anode structure 14
while within the fixture 30 is to coat the surface of the anode
structure 14 that contacted the inner region 38 with pigment
particles. When the anode structure 14 is removed from the fixture
30, the pigment particles remain adhered to the anode structure 14.
If the pigment particles are not completely dry on the anode
structure 14, the anode structure 14 should be left in a horizontal
position until the fluid has completely evaporated, as indicated by
block 49.
Once the pigment particles have been dried on the anode structure
14, the anode structure 14 is assembled into a EPID such as EPID 10
in FIG. 1. The assembled EPID is lacking suspension fluid and fill
holes are left in the construction of the EPID for that purpose.
Once assembled, as indicated by block 51, the EPID 10 is placed in
a vacuum chamber. The pressure within the vacuum chamber is then
reduced and the EPID 10 is submerged within a volume of a
suspension fluid. The pressure within the vacuum chamber is then
slowly raised to ambient pressure causing the suspension fluid to
fill the EPID 10 as indicated by block 53. The fill holes used to
fill the EPID 10 with suspension fluid are then closed and an
appropriate voltage, as indicated by block 55, is applied to the
anode structure 14 and the cathode structure 16 of the EPID 10. The
voltage applied creates an opposite electrophoretic effect thereby
causing the pigment particles to leave the anode structure and
become dispersed within the suspension fluid.
By coating the anode structure 14 with pigment particles prior to
the assembly of the EPID 10, the EPID 10 can be manufactured having
any anode to cathode spacing without concern for achieving a proper
pigment particle concentration upon the application of a dispersion
medium. Consequently, EPIDs having spacings of below 0.007 inches
or even below 0.003 inches can readily be manufactured.
In the described method the anode structure 14 of the EPID was
coated with pigment particles. It should be understood by a person
skilled in the art that the cathode structure 16 of the EPID 10
could be coated with pigment particles in place and stead of the
anode structure 14 by placing the cathode structure 16 into the
fixture 30. However, the use of the anode structure 14 is preferred
because the anode structure is conventionally less intricate than
is a cathode structure and is more readily handled and coupled to
the power supply 44.
It will be understood that the method of filling a EPID described
herein is merely exemplary and that a person skilled in the art may
make many variations and modifications to the described embodiment
utilizing functionally equivalent components to those described.
More specifically, it should be understood that the fixture 30
described can be formed in any manner, provided it has the ability
to retain a small reservoir of fluid and has a base surface that
can act as a cathode during an electrophoretic reaction. All such
variations and modifications are intended to be included within the
scope of the invention as defined by the appended claims.
* * * * *